How to create a drop down that offers multiple percentage choices for an entire column

Hello all. I am creating a bid sheet and would like to have on my header column a cell that is titled "%Profit". I would like to be able to click on that header cell and have drop down options which allow me to choose between varying percentages (%50,60%,65%), click on desired percentage, and have my choice applied to all of the amounts in the column directly below. There are several places I would like to apply this type of function on my sheet, but for this example, the details are as follows: The header "%Profit" cell is G1. This column continues down to G19. The previous column, "Cost" Is F1-F19. My goal is to apply which ever percentage I choose in my drop down category of G1 to the cost given in the "F" column. I hope this is clear and that what I would like to achieve is even a possibility. Thank you to anyone who may be able to provide some insight. -WFK

Thank you Ford, unfortunately that just didn't clear anything up for me.

So i click on the G1 cell "Profit%", where i want the drop down to be. Then i go to "data validation" like you advised.
I click on "allow" and select "list" from the options. Now it asks me to enter a "source", which i believe to be the function code.
Alas, this is where i get stuck. What do i input so it allows me to enter in multiple formulas to choose from and what shall the formulas
be? Like i said, id like to do this in several places on my sheet, so understanding how to make the formula would be a plus.
Thank you so much for your time!

What you need to do first is pick some cells in your spreadsheet (can be anywhere) to contain the various percentages you want as the list.
For example, you can put into cell Z1 "50%", for cell Z2 "60%", and for cell Z3 "65%".
Go back and click on cell G1 to apply data validation, and for the Source you put in "$Z$1:$Z$3" (or click on the button to the right of the Source input field to select the cells directly).

Now you should get a dropdown for cell G1 that lists the three percentages to choose from.
In cell G2, enter "=F2*$G$1". Then copy cell G2 and paste the formula on cells G3 to G19.

That did it. Thank you both for your help and teaching me how to fish